Methods for filling electrical apparatus with potting material



July 14; 1964 R. H' PARSONS METHGDS FOR FILLING ELECTRICAL APPARATUSWITH POTTING MATERIAL 4 Sheets-Sheet 1 Filed June Ev, 1961 [fit 627C3 1Faber' /7. 29119 0175 July 14, 1964 R. H. PARSONS METHODS FOR FILLINGELECTRICAL APPARATUS WITH FOTTING MATERIAL Filed June 5, 1961 4Sheets-Sheet" 2i July 14, 1964 R. H. PARSONS 3,141,049

METHODS FOR FILLING ELECTRICAL. APPARATUS WITH POTTING MATERIAL FiledJune 5, 1961 4 Sheets-Sheet L5 y 1964 R. H. PARSONS 3,141,049

METHODS FOR FILLING ELECTRICAL APPARATUS WITH PUTTING MATERIAL FiledJune 5, 1961 4 Sheets-Sheet 4 8411.457 CASE WITH ("Vii/Z1075 PIMVIDASSEMBZl-D ,wopamm auusr Attorney- United States Patent 3,141,049METHODS FOR FILLING ELECTRECAL APPA- RATUS WITH PUTTING MATERIAL RobertH. Parsons, Danville, Ill., assignor to General Electric Company, acorporation of New York Filed June 5, 1961, Ser. No. 114,855 8 Claims.(Cl. 264-138) The present invention relates to methods for fillingelectrical apparatus with potting material and more particularly, tosuch methods especially usable with ballast apparatus. It relatesspecifically to such methods wherein hardenable liquid potting materialis poured over the ballast apparatus and is solidified to provide asuitable encapsulant for the components of the apparatus.

Ballast apparatus or ballasts for starting and operating fluorescentlamps are generally housed in metallic cases or canisters which serve asreceptacles for the potting material in which the apparatus is embeddedand as protective enclosures for the components and internal circuitconnections thereof. Commonly used potting materials are mixtures ofmineral filler and asphaltic compounds. The asphaltic compounds areacceptable constituents of the potting materials since they possess gooddielectric properties. Also, they possess good sound dampeningcharacteristics and relatively low melting temperatures. Sand is usedprimarily as a filler. Since the potting materials are applied to theapparatus in a liquid state by pouring, it is required that they haverelatively low melting temperatures so that the liquid potting materialwill not cause damage to the components of the apparatus.

In order to obtain good heat dissipation and to minimize noise producedby the electromagnetic components of the ballast apparatus, it isnecessary that the potting material filling the ballast case be free ofvoids and that the ballast case be completely filled with the pottingmaterial to provide good thermal contact between the potting materialused and the ballast case. Void formations impair the ability of thepotting material to dampen noise developed in the components and alsoserve as an insulating barrier to the transfer of heat from thecomponents. Generally, the heat generated by the components of theballast apparatus is dissipated through the potting material and thecase to the lamp fixture to which the ballast apparatus is attached andalso to the surrounding environment of the ballast case and lampfixture. Unless the heat generated is eifectively removed, prematurefailures of the ballast apparatus may occur.

The cover plate of the ballast case usually serves as the mountingsurface for attaching the ballast apparatus to the lamp fixture. In someapplications the coils of the ballast transformer are arranged so thatthe coil sides are disposed close to the coverplate to provide for moreeffective dissipation of heat to the lamp fixture which serves as a heatsink. In such applications it is particularly important that thecoverplate of the ballast case be in good thermal contact with thepotting material.

In order to insure that good thermal contact is obtained between thecoverplate and potting material when it is assembled thereon, it isnecessary that the ballast case be completely filled with a pottingmaterial up to the upper edges of the sides forming the ballast case sothat when the coverplate is applied to the top thereof, there is no airspace between the coverplate and the upper surface of the pottingmaterial filling the case.

Heretofore, the methods employed for filling a ballast case with pottingmaterial have not provided a suitable means for assuring that thepotting material was filled up exactly to the level of the coverplateand in good thermal contact therewith. Conventional methods for fillingapparatus with potting material by gravity fiow and relyice ing onmanual control have the inherent disadvantage that the level of thepotting material in the ballast cannot be precisely controlled. In suchmethods of filling, the potting material must be poured very rapidlyinto the ballast case in order to prevent hardening that would interferewith good penetration of the potting material into the apparatus.Frequently, the hot potting material bubbles and splatters. Also, thesupply of liquid potting material must be turned off before the level ofthe liquid potting material reaches the top edges of the sides of theballast case and spills over. Thus, the potting material generally doesnot completely fill the ballast case.

After the supply of potting material is turned oil, the potting materialis allowed to cool and solidify. During the cooling period a certainamount of penetration of the potting material into the components of theballast apparatus continues to take place. Also, the potting materialitself shrinks during cooling. Consequently, the level of the pottingmaterial in the ballast case is lowered. When the coverplate isassembled on the ballast case, the potting material does not completelyfill the ballast case and an air space or void exists between the uppersurface of the potting material and the coverplate.

Prior art methods utilizing pressure filling apparatus also pose aproblem insofar as complete filling of the ballast case is concerned. Insuch methods, the liquid potting material is inserted into the ballastcase through an opening in the coverplate which is assembled on theballast case prior to the potting operation. Due to shrinkage andentrainment of air between the ballast case and top surface of thepotting material, voids are formed between the top surface of thepotting material and the coverplate. Thus, methods of the prior art havenot been satisfactory in applications where it is required that the topsurface of the potting material filling the ballast be in good thermalcontact with the coverplate.

It is, therefore, desirable that a method be provided for filling anenclosed electrical apparatus with potting material wherein the pottingmaterial is completely filled to the top level of the ballast case sothat the coverplate, when assembled thereon, is brought into goodthermal contact with the upper surface of the potting material. Further,it is also desirable that the method be readily adaptable to massproduction techniques so that the appa ratus can be automatically andcontinuously filled with potting material in an automated type ofassembly opera tion.

Accordingly, it is a general object of the invention to provide animproved method for filling an encased electrical apparatus with aninsulating potting material.

It is a more specific object of my invention to provide an improvedmethod for filling the case of a ballast apparatus with potting materialwherein the case is completely filled between the upper surface of thepotting material and the coverplate of the ballast case.

It is still a further object of my invention to provide an improvedmethod for filling a ballast apparatus with potting material which isreadily adaptable to automated assembly techniques.

According to one form of my invention I have provided an improved methodfor filling the case housing electrical apparatus with a pottingmaterial, such as a mixture of asphalt and sand, which includes thesteps of filling the case with liquid potting material until an overfiowis obtained at the top "thereof. The potting material adjacent to theouter edges of the overflow is solidified or hardened and forms aconfining barrier for the liquid potting material. Then, the liquidpotting material is allowed to sufficiently harden in order that theoverflow of potting material can be removed as by a slicing operation.With the overflow of potting material sliced off, the case is filledwith potting material to 3 the top thereof assuring good contact withthe cover plate when it is attached.

In another aspect of the invention I have provided a retaining means forthe overflow of potting material at the top of the case. Simultaneously,the retaining means is cooled to a predetermined temperature so that thepotting material adjacent to the retaining means hardens to form aconfining barrier for the liquid potting material. It has been foundthat by cooling the retaining means, the potting material does notadhere to the retaining means. The retaining means is removed when theconfining barrier of hardened potting material is formed. The liquidpotting material is then allowed to harden sufficiently to permit theoverflow of potting material to be sliced off. Where a cutting blade isused to slice oif the overflow, it has been found that cooling thecutting blade will also prevent potting material from adhering to theblade.

The subject matter which I regard as my invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. My invention, however, both as to organization and modeof operation, together with further objects and advantages thereof, maybe best understood by reference to the following description taken inconjunction with the accompanying drawings in which:

FIG. 1 is an illustration of a conventional ballast apparatus with thecoverplate removed prior to the potting operation;

FIG. 2 shows the ballast apparatus of FIG. 1 in position at the pottingmaterial filling station with the overflow collar in "the loweredposition;

FIG. 3 shows the ballast apparatus of FIG. 1 wherein the case has beenfilled with the liquid potting compound until an overflow of pottingmaterial was obtained at the top thereof;

FIG. 4 is a sectional view taken along line 4- 3 of the ballastapparatus illustrated in FIG. 3 showing how the potting materialadjacent to the overflow collar is hardened to form a confining barrierfor the overflow of liquid potting material;

FIG. 5 shows the overflow collar in a raised position, the hardenedouter edge of potting material preventing the liquid overflow of pottingmaterial from spilling;

FIG. 6 illustrates the ballast apparatus at the slicing station whereinthe overflow of the potting compound is being removed by slicing off theoverflow with a blade which is guided by the upper edges of the sides ofthe ballast case;

FIG. 7 shows a coverplate being attached to the ballast case in thefinal assembly operation; and

FIG. 8 illustrates diagrammatically with legends the sequence of thevarious steps of the method according to one form of the invention, themethod being carried out on a continuous conveyor system.

In FIGS. 1 through 7 of the drawings, I have illustrated the consecutivesteps of the method in accordance with one embodiment of the inventionbeing performed on a ballast apparatus 14). As shown in FIG. 1, theballast apparatus 11 is completely assembled except that the ballastapparatus 10 is not potted. It will be seen that the ballast apparatus10 includes a ballast case 11 having four sides, a bottom and a top orcoverplate which has not been assembled so that potting material can bepoured into the ballast case 11. Disposed within the ballast case 11 arethe components of the ballast apparatus 10, which includes a capacitor12, a ballast transformer 13 having a pair of coils 14, 15 mounted on amagnetic core 16, and various electrical leads.

It will be noted that the ballast transformer 13 is disposed so that theinternal connections to the coils 14, 15 are made on the top side of thecoils 14, 15. If desired, the ballast transformer 13 may be inserted inthe ballast case in an upside down arrangement wherein the internalconnections to the coils 14, 15 of the ballast transformer 13 would beon the under side of the coils 14, 15. Where the internal connectionsare made in such a manner, it will be seen that the coils would bedisposed closer to the coverplate when it is assembled on the ballastcase 11. In such an arrangement, interference to heat transfer betweenthe coils and the coverplate is minimized. Thus, it will be appreciatedthat the method of the invention is readily adaptable to variousarrangements of the components in a ballast apparatus and it is notintended by the apparatus employed in the illustrative embodiment tolimit the invention thereto.

The ballast apparatus 10, as shown in the drawings, is carried on aconveyor 17 illustrated diagrammatically to show how the method of theinvention may be carried out as a continuous operation. A suitablepositioning means 13 is provided to maintain the ballast apparatus 10 inposition on the conveyor 17 as the method is carried out. Although thesteps of the method of the invention are shown performed on a singleballast apparatus 10, it will be understood that the steps of the methodof this invention can be simultaneously performed on a plurality ofballasts.

In FIG. 2, I have shown the ballast apparatus in position at the pottingmaterial filling station. As shown in outline, an overflow collar 19 islowered from an elevated position and brought down in position on theballast case 11. Although in the illustrative embodiment of theinvention, the overflow collar 19 is inserted on the ballast case 11, itwill be undenstood that the overflow collar 19 can readily be maintainedin a fixed position and the ballast apparatus 10 brought into positionunder the overflow collar 1?. A cooling means having an inlet 22 and anoutlet 21 is provided for the passage of cooling fluid around theoverflow collar 19. In the exemplification of the invention anantifreeze solution having an ethylene glycol base was used as a coolingfluid and was supplied to the overflow collar 19 at a temperature ofapproximately minus five degrees centigrade.

It will be noted that the overflow collar 19 which serves as a retainingmeans for the overflow of potting material on the top of the ballastcase 11, has a rectangular configuration that substantially conforms tothe configuration of the ballast case 11 so that when it is placed inposition on top thereof, it forms an extension of the ballast case 11and effectively contains or confines the overflow of potting material.The inner sides of the overflow collar 19 were inclined inwardly atdraft angle of approximately seven degrees in order to permit theoverflow collar 19 to be readily removed from the potting material.

A filling nozzle 25 connected with a tank (not shown) containing theliquid potting material is located above the apparatus 10. In theexemplification of the invention, a hardenable asphalt and sand mixturewas used in the potting operation and Was heated to a temperature of 200degrees centigrade. A valve means 26 is provided to control the flow ofthe liquid potting material supplied to the ballast apparatus 10. Asseen in FIG. 2, the valve means 26 is in the closed position and nopotting material is being injected into the ballast case. Leads 27, 28connected with valve means 26 are provided in order that valve means 26can be actuated either manually or automatically from a remote location.

A shown in FIG. 3, the valve means 26 is open and hot liquid pottingmaterial 29 is being poured into the ballast case 11. In accordance withthe invention the potting material 2? is poured until an overflow isobtained, the overflow being contained by the overflow collar 19.Bringing the liquid potting material 29 up to a level above the ballastcase 11 insures that the apparatus is completely filled with pottingmaterial 29. Since a cooling fluid is circulated through the overflowcollar 19, the liquid potting material adjacent to the overflow collar19 solidifies much sooner than the rest of the liquid potting materialin the ballast case 11. It was found that by cooling the overflow collar19, the potting material in contact with the overflow collar 19 did notadhere thereto, and the overfiow collar 19 could be readily removed fromthe potting material after the potting material adjacent to the overflowcollar 19 hardens. Further it was found that by hardening or solidifyingthe potting compound adjacent to the cooling collar 19, a confiningbarrier is formed which can contain the overflow of liquid pottingmaterial during the period that the rest of the liquid potting materialsolidifies. By causing the potting material adjacent to the overflowcollar 19 to be initially solidified, it is possible to remove theoverflow collar 19 in a relatively short period of time.

In the method used to exemplify the invention, the potting materialadjacent to the outer edges of the overflow collar 19 was sufficientlyhardened within approximately one minute and the overflow collar 19 wasthen removed from the ballast case 11. It will be apparent that thearrangement of the present invention makes it possible to continuouslyremove and apply the overflow collar 19 in an automated type of assemblyoperation. Although I have only shown a single ballast apparatus toillustrate the filling step, in the exemplification of the invention agroup of ten ballasts were simultaneously filled and cooled at one time.Thus, it will be apparent that the steps of the method of the inventioncan be performed simultaneously on a plurality of ballasts.

In FIG. 4, I have illustrated a sectional view of the ballast apparatus10 showing the formation of a confining barrier 31 containing liquidpotting material 32. It will be seen that most of the potting materialwithin the interior of the ballast apparatus 1t is in a liquid state. Byinitially hardening only the potting material 31 adjacent to theoverflow collar 19, sufiicient time is afforded to allow the hot liquidpotting material to effectively saturate the magnetic core 1%, the coil14 and the other components of the ballast apparatus ltl.

Continuing now with the description of the method of the invention, itwill be seen that in FIG. 5, I have illustrated the ballast case 11 atthe potting material filling station with the overflow collar 19 and thefilling nozzle 25 in the raised position. The valve means 26 has beenshut off. At this point, only the outer edges of the potting materialadjacent to the overflow collar 19 have hardened and the confiningbarrier 31 of the hardened or solidified potting material now serves asa retaining means for the overflow of liquid potting material 32. Theballast apparatus It) is now ready for delivery by the conveyor 17 tothe slicing station.

Before the slicing operation can be performed, sufficient time must beallowed to permit the potting material to cool and sufficiently hardenor solidify so that the slicing operation can be performed. In themethod used to exemplify the invention, it was found that approximately5 minutes were required for the potting compound to cool at roomtemperature. If desired, the period of time required for the liquidpotting material to harden may be shortened by the provision of acooling means to increase the rate of heat transfer from the liquidpotting material 32.

In FIG. 6, the ballast apparatus It) is shown at the slicing stationwhere the step of slicing off the overflow 33 of hardened pottingmaterial is carried out. A cutting, blade 34 having a cutting edge 36,is passed along the edges 37, 38 of the side walls of the ballast case11 and the overflow 33 is sliced off in this way. The cutting edge 36may, preferably, be shaped or contoured so that the potting material isabove the edges 37, 38 of the ballast case 11 and so that a good contactis assured when the coverplate 42 is attached. It was found that bysimultaneously cooling the cutting blade 34 by circulating cooling fluidthrough ducts 39, 40 formed therein, it was possible to prevent pottingmaterial from adhering to the cutting blade thereby permitting the blade34 to be used in a continuous operation. The outer edges 37, 33 may beused to serve as a guide means to insure that the overflow 33 is cut offprecisely at the level of or at a level slightly higher than the upperedges 37, 38. When the coverplate of the ballast case 11 is placed inassembled relation on the ballast case 11, a good physical contact isobtained between the coverplate and the potting material. It will beseen that when the overflow 33 is completely sliced off, as is shown inoutline in FIG. 6, the slicing off overflow 33 falls off on a conveyor41 where it can be conveniently returned to the tank (not shown)containing the liquid potting material and reused.

In accordance with the method of the present invention, it was possibleto fill a ballast case used to house a conentional ballast used to startand operate two 40 watt rapid start fluorescent lamps with 11.6 ouncesof asphaltic potting material. By manually filling an identical ballastapparatus, it was found that the ballast case could be filled withapproximately 9.6 ounces of asphaltic potting material. Thus, it will beappreciated that the method of the present invention makes it possibleto fill a ballast case with 20 percent by weight more asphaltic pottingmaterial than by manually controlled gravity flow meth ods. Thus, it isapparent that the ballast case 11 is more completely filled with pottinmaterial by the method of the present invention. Since the pottingmaterial is sliced off at or above the level of the upper edges 37, 38of the sides of the ballast case, the top surface of the pottingmaterial is brought into good thermal contact with the coverplate andpotting material which completely fills the case 11. This arrangementprovides the advantage that the heat generated by the ballast componentscan be more effectively dissipated from the ballast apparatus,particularly in applications where the fixture is utilized as a heatsink and the coverplate is attached to the fixture.

Referring to FIG. 7, there is illustrated the ballast apparatus 10 whichis now filled with potting material. It will be seen that the coverplate42 is attached to the ballast case 11 by attaching the eyelets 43, 44,45, 46 thereto and that the coverplate 42 covers the top surface of thehardened potting material 47. Since the top surface of the hardenedpotting material 47 is level or slightly higher with the upper edges 37,33 of the sides of ballast case 11, good physical contact results whencoverplate 42 is assembled thereon.

Having reference now to FIG. 8, I have illustrated thereindiagrammatically the combined sequence of steps of the method accordingto one form of the invention and have briefly summarized in the legends,the sequence of the operations performed. As shown therein, the ballastcase 10 is positioned on the conveyor 17 at station A with thecoverplate removed. At station B, the overflow collar 19 and the fillingnozzle 25 are lowered in position over the ballast case 11. Liquidpotting material is poured into the ballast case 11 until an overflow ofpotting material is obtained at the top thereof. Simultaneously, acooling fluid is circulated through the overflow collar 19 in order toharden the potting material adjacent thereto and to form a confiningbarrier for the liquid potting material. After the potting materialadjacent to the overflow collar 19 has hardened sufficiently so that itcan retain the liquid potting material, the overflow collar 19 andfilling nozzle 25 are raised. At station C, further solidification ofthe liquid potting material is carried out. Depending upon theparticular potting material used, the step of solidification may becarried out at room temperature, as was done in the hereinbeforedescribed exemplification of the invention wherein the potting materialcon- .tained asphaltic compounds as a constituent thereof. It

When the potting material has sufiiciently solidified so that it can besliced off, the ballast apparatus 10 is conveyed to the slicing stationD. The cutting blade 34 has a cutting edge which is passed along thesides of the ballast case 11 to slice off the overflow 33 of pottingmaterial. Simultaneously, the cutting blade 34 is kept at a relativelycool temperature by circulating cooling fluid through the tubes 39, 40.After this step is completed, the coverplate 42 is assembled on the topof the ballast case 11 as shown at station B. At station F the assembledand potted ballast apparatus 10 is shown.

In the exemplification of the invention, a potting material containing53 percent silica and 47 percent asphaltic compounds was employed andwas poured into the ballast case 11 at a temperature of 200 degreescentigrade. Although I have described my invention in connection with anasphaltic potting material, it will be appreciated that the otherhardenable insulating materials, which can be rendered liquid atrelatively low temperatures and solidify at room temperature either withor without catalyst, may be employed. The method is particularlyadaptable to the potting materials containing asphaltic compounds whichare difficult to handle. A principal advantage of the method of theinvention is that a ballast apparatus can be readily filled to the levelof or slightly above the upper edges of the sides thereof to provide agood thermal contact between the upper surface of the potting materialand the coverplate of the ballast case. Another advantage of the methodof the invention is that the overflow of potting material takes up theshrinkage that normally occurs during cooling. Splattering caused by thebubbling of the hot potting material during filling is minimized by theoverflow collar. Further, the method readily lends itself to automatedassembly techniques.

It will be apparent that the sequence of steps of the method which Ihave described herein by way of an exemplification of the invention maybe changed or varied without departing from the principle of theinvention. It is to be understood, therefore, that I intend by theappended claims to cover all such changes and modifications that fallwithin the true spirit and scope or" the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A method for filling the case of a ballast apparatus with pottingmaterial comprising the steps of applying a retaining means on theballast case for containing an overflow of potting material, pouringliquid potting material into the case so that the potting material fillsthe case and overflows within said retaining means, causing the pottingmaterial adjacent to said retaining means to harden sufficiently so thatthe overflow of liquid potting material can be contained by saidhardened potting material without said retaining means, causing saidretaining means to be separated from said ballast case and said pottingmaterial, allowing said liquid potting material to harden, and slicingoff the overflow of said potting material so that the potting materialfills the ballast case, and attaching a coverplate to the case so thatthe coverplate lies along the surface formed by slicing off the overflowof potting material.

2. A method for filling the case of an electrical apparatus with ahardenable potting material, said method comprising the steps of pouringliquid hardenable potting material into the case until an overflow iscontained at the top thereof, restraining said overflow from spilling,hardening the potting material adjacent to the outer edges of saidoverflow so that the potting material adjacent thereto forms a confiningbarrier for the liquid potting material, causing the liquid pottingmaterial to harden sufficiently so that the overflow thereof can beremoved by slicing, slicing the overflow of the potting material so thatthe case is filled to the top level thereof, and assembling a coverplateon said case so that the coverplate lies along the surface formed byslicing said overflow.

3. A method for filling the case of a ballast apparatus with ahardenable insulating potting material containing an asphaltic compoundas a constituent thereof, said method comprising the steps of fillingthe case with liquid potting material until an overflow is obtained atthe top thereof, confining said overflow of potting material at the topthereof, cooling the outer edges of said overflow of material for aperiod of time suflicient to cause the potting material adjacent to theouter edges to harden and form a confining barrier to contain saidliquid overflow and prevent spillage thereof, allowing said pottingmaterial to harden sufficiently so that the overflow of potting materialcan be sliced oil, and slicing off the overflow of potting materialsubstantially level with the top of said ballast case and attaching acoverplate to said ballast case so that the coverplate is in intimatecontact with the surface of said potting material formed by slicing oldthe overflow portion thereof.

4. A method for filling the case of a ballast apparatus with a pottingmaterial containing an asphaltic compound as a constituent, saidmaterial liquefying when heated to a predetermined temperature, saidmethod comprising the steps of heating said potting material to a liquidstate, pouring said liquid potting material into the case until anoverflow is obtained at the top thereof, cooling the potting materialadjacent to the outer edges of said overflow to cause the pottingmaterial adjacent to said outer edges of the overflow to harden and forma confining barrier for the liquid potting material, cooling the liquidpotting material until it suificiently hardens so that the overflowthereof can be removed by slicing, slicing off the overflow of pottingmaterial whereby the case is filled to the top thereof, and assembling acoverplate so that the coverplate lies along the surface formed byslicing off the overflow of potting material.

5. A method for filling the case of an electrical apparatus with apotting material containing an asphaltic compound comprising the stepsof applying a retaining means on the case for confining the overflow ofpotting material at the top thereof, pouring heated liquid pottingmaterial into the case until the potting material fills the case andoverflow is contained within said retaining means and simultaneouslycooling said retaining means to cause the potting material adjacent tosaid retaining means to harden and to permit said retaining means to beseparated from said potting material without potting material adheringthereto, separating said retaining means from said ballast case and saidpotting material when said potting material adjacent to said retainingmeans has hardened sufficiently so that the overflow of liquid pottingmaterial is contained by said hardened potting material without saidretaining means, causing the liquid potting material to suflicientlyharden so that the overflow thereof can be removed by slicing, slicingoif the overflow of the potting material substantially level with thetop of the case and attaching a coverplate to said case.

6. A method for filling the case of a ballast apparatus with pottingmaterial, said case having four sides, a bottom and a coverplate, saidmethod comprising the steps of filling the case with liquid pottingmaterial through the opening provided for the coverplate until anoverflow is contained at the top thereof, causing the outer edges ofsaid overflow of potting material to harden so that the potting materialadjacent to the outer edges of the overflow forms a confining barrierfor the liquid potting material, cooling the liquid potting material atleast until it is sulficiently hardened so that the overflow thereof canbe removed by slicing, passing a cutting blade having a cutting edgealong the upper edges of at least two of the sides of the case to sliceoff the overflow of potting material whereby the case is filled withpotting material to the top thereof and attaching the coverplate to thecase.

7. A method for filling the ballast case of a ballast apparatus withpotting material containing an asphaltic compound as a constituentthereof, said ballast case being formed of four sides, a bottom and acoverplate, said method comprising the steps of pouring liquid pottingmaterial into the case with the coverplate removed until an overflow isobtained at the top thereof, confining the overflow of potting materialat the top of said case and simultaneously cooling the outer edges ofthe overflow in order to harden the potting material adjacent to theouter edges thereof and form a confining barrier for the liquidoverflow, hardening the liquid potting material at least sufficiently sothat the overflow thereof can be removed by slicing, passing a cuttingblade having a cutting edge along the upper edges of at least two sidesof said ballast case to slice off the overflow of potting material sothat the ballast case is filled to the top thereof, and attaching thecoverplate to the ballast case so that the cover plate lies along thesurface formed by slicing the overflow of potting material.

8. A method for filling the ballast case of a ballast apparatus withpotting material containing an asphaltic compound as a constituentthereof, said ballast case having four sides, a bottom and a coverplate,said method comprising the steps of filling the case with liquid pottingmaterial through the opening provided for the coverplate 10 until anoverflow is contained at the top thereof, confining the overflow ofpotting material and simultaneously cooling the outer edges of theoverflow to form a confining barrier for the liquid overflow, hardeningthe liquid potting material at least sutficiently so that the overflowcan be removed by slicing, passing a cutting blade having a cutting edgealong the upper edges of at least two sides of the ballast case to sliceoil said overflow and simultaneously cooling said cutting blade toprevent potting material from adhering thereto, and attaching thecoverplate to the case so that the coverplate lies along the surfaceformed by slicing ofl the overflow of potting material.

References Cited in the file of this patent UNITED STATES PATENTS2,063,315 Kuettel Dec. 8, 1936 2,136,423 Fields et al. Nov. 15, 19382,373,593 Pease Apr. 10, 1945 2,432,981 Abrahams et a1 Dec. 23, 19472,874,407 Chabot et a1 Feb. 24, 1959 2,957,207 Roop et al. Oct. 25, 19602,978,782 Wagner Apr. 11, 1961

1. A METHOD FOR FILLING THE CASE OF A BALLAST APPARATUS WITH POTTINGMATERIAL COMPRISING THE STEPS OF APPLYING A RETAINING MEANS ON THEBALLAST CASE FOR CONTAINING AN OVERFLOW OF POTTING MATERIAL, POURINGLIQUID POTTING MATERIAL INTO THE CASE SO THAT THE POTTING MATERIAL FILLSTHE CASE AND OVERFLOWS WITHIN SAID RETAINING MEANS, CAUSING THE POTTINGMATERIAL ADJACENT TO SAID RETAINING MEANS TO HARDEN SUFFICIENTLY SO THATTHE OVERFLOW OF LIQUID POTTING MATERIAL CAN BE CONTAINED BY SAIDHARDENED POTTING MATERIAL WITHOUT SAID RETAINING MEANS, CAUSING SAIDRETAINING MEANS TO BE SEPARATED FROM SAID BALLAST CASE AND SAID POTTINGMATERIAL, ALLOWING SAID LIQUID POTTING MATERIAL TO HARDEN, AND SLICINGOFF THE OVERFLOW OF SAID POTTING MATERIAL SO THAT THE POTTING MATERIALFILLS THE BALLAST CASE, AND ATTACHING A COVERPLATE TO THE CASE SO THATTHE COVERPLATE LIES ALONG THE SURFACE FORMED BY SLICING OFF THE OVERFLOWOF POTTING MATERIAL.